The present invention relates to serial data communications generally and, more particularly, to a methodology for the synchronization of super frames in an integrated services digital broadcasting for satellites (ISDB-S) system.
Data may be serially transmitted one bit at a time along a data transmission path. The serial data can be transmitted in groups of bits called frames. The frames are delimited by synchronization codes that identify the beginning or the end of each frame. The synchronization codes must be identified in the data stream before the significance of the data contained in the frame can be determined. When a synchronization code is identified, a signal can be generated to synchronize a data recovery circuit to the contents of the frame. The synchronization of the data recovery circuit to the frame is frame synchronization. The frames can be grouped into super frames. The synchronization of a super frame is super frame synchronization.
Referring to FIG. 1, a diagram of a satellite transmission system 10 illustrating a satellite data transmission path is shown. A data signal 12 is sent using electromagnetic waves from an uplink station 14 to a satellite 16. The data signal 12 can contain one or more integrated services digital broadcasting for satellites (ISDB-S) system super frames. The satellite 16 can recover the data from the data signal 12 and/or relay the data signal 12 using electromagnetic waves to a downlink ground station 18. The ground station 18 can recover the data from the data signal 12. Both the satellite 16 and the ground station 18 can use a data recovery circuit that is synchronized to the data signal 12 by a synchronization detector circuit. Since the data signal 12 is sent using electromagnetic waves, the data signal 12 can contain noise. A measurement of a power ratio between signal and noise acquired by the data signal 12 is the signal-to-noise ratio (SNR). As the SNR of the signal 12 decreases, synchronization and data recovery become more difficult.
Referring to FIG. 2, a diagram of an ISDB-S super frame 20 is shown. In an integrated services digital broadcasting for satellites (ISDB-S) system, frame structure is organized into super frames 20. Each super frame contains eight frames 22a-22g. Each frame has an embedded unique word W1 (e.g., ECD28h) in its header to identify the start of the frame 22. In addition, the first frame 22a of a super frame 20 has a unique word W2 (e.g., OB677h) in its header to identify the start of the super frame 20. Each of the subsequent seven frames 22b-22g have a unique word W3 (e.g., F4988h) in the same position as the unique word W2 in the first frame 22a. The unique words W2 and W3 are digital complements of each other (e.g., W2=!W3).
In a conventional method of super frame synchronization, a state machine is constructed based on the detection of only the unique word W2. The embedded unique words W3 are not used in super frame synchronization. Using only the unique word W2 to acquire super frame synchronization has the disadvantage of a high false lock probability, especially in a low signal-to-noise ratio (SNR) environment. Since the super frame is quite large, a high probability of false lock makes super frame synchronization based on a single unique word unreliable. A solution is needed to provide a reliable super frame synchronization.
The present invention concerns an apparatus comprising a first circuit and a second circuit. The first circuit may be configured to generate a first detection signal and a second detection signal in response to (i) an input signal, (ii) a first control signal, and (iii) a second control signal. The second circuit may be configured to generate a first output signal and a second output signal in response to (i) the first detection signal, (ii) the second detection signal, and (iii) a third control signal.
The objects, features and advantages of the present invention include providing a method of synchronizing super frames in an integrated services digital broadcasting for satellites (ISDB-S) system that may (i) reduce the probability of false locks, (ii) detect two unique words, (iii) use one detection region for detecting two unique words, (iv) use one unique word detector to detect two unique words, (v) adjust parameters in response to a signal-to-noise ration, and/or (vi) provide a more reliable frame synchronization.